Electromagnetic valve for controlling the flow of a fluid in a pipe

ABSTRACT

Electromagnetic valve for controlling the flow of a liquid metal or metal alloy in a pressurized pipe is provided with a tubular body made of a material which is permeable to magnetic fields, and a polyphase field coil arranged around the tubular body in order to create a magnetic field for sliding lengthwise along the tubular body. A core is held in an axial position through the tubular body, with the core leaving between itself and the inner surface of the tubular body a substantially annular passage for the liquid metal or metal alloy of which the flow is to be controlled.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electromagnetic valve forcontrolling the flow of a metal or metal alloy in liquid phase in a pipeunder load, comprising a tubular body made of a material permeable tothe magnetic field and at least one polyphase field coil arranged aroundthe tubular body in order to create a magnetic field sliding lengthwisealong the tubular body.

2. Discussion of Background Information

In the field of metallurgy, for example, in an industrial castingequipment or in equipment for covering iron and steel products with acoating of metal or metal alloy, such as hot galvanization equipment, orin other applications, it is often necessary to be able to control aflow of metal or metal alloy in liquid phase. In this respect, eitherthe metal or the metal alloy is in molten state following a controlledincrease of its temperature, or the metal or metal alloy is normallyliquid at ambient temperature which is the case, for example withmercury. In order to control a flow of liquid metal or metal alloy, itis usual to use electromechanical or hydromechanical systems such asnozzles with slide valve, stopper rods, etc. These systems involveconsiderable investment and relatively high maintenance costs due to thepresence of movable mechanical elements in these systems.

It is for this reason that electromagnetic valves have been proposed forsome time which do not comprise any movable mechanical elements forcontrolling the flow of a metal or metal alloy in liquid phase in a pipeunder load. The electromagnetic valves of his patent operate inaccordance with a principle similar to that of a linear motor. The roleof the mobile armature is performed by the metal or metal alloy whoseflow is to be controlled. In these electromagnetic valves, the polyphasefield coil is disposed and electrically connected so that the magneticfield that it generates propagates in counter-flow with respect to thenormal flow direction of the liquid metal or metal alloy in the pipeunder load. In other words, the magnetomotive force generated by thepolyphase field coil and applied to the liquid metal in the pipe opposesthe force due to the hydrostatic pressure of the liquid metal in thepipe. By adjusting the intensity of the current in the polyphase coil,it is possible to regulate the flow rate of the liquid metal or metalalloy in the pipe. The greater is the intensity of the current in thepolyphase coil, the lower the flow rate of the liquid metal or metalalloy flowing through the electromagnetic valve. Theoretically, by usinga sufficiently intense current, it is possible to stop the flow of theliquid metal or metal alloy arriving at the valve. However, theintensity of the current necessary for stopping the flow of metal liquidor metal alloy is relatively great. Therefore, because the electricalpower necessary for maintaining the electromagnetic valve in the"closed" state is great, it has proved difficult to obtain a completereliable stop of the flow of liquid metal or metal alloy.

In order to obtain a complete stoppage of the flow of liquid metal ormetal alloy, it has been proposed to partially close the outlet end ofthe tubular body of the electromagnetic valve by a transverse wallpresenting an outlet orifice offset or off-center with respect to thelongitudinal axis of the tubular body. Although such an arrangementeffectively insures complete stop of the flow of liquid metal or metalalloy, the intensity of the current necessary for that purpose remainsrelatively high. In addition, when the electromagnetic valve is"opened", the transverse wall with its off-center outlet orifice causesdisturbances (turbulence) and pressure drops in the flow of liquid metalor metal alloy which, in certain applications, may be unacceptable.

SUMMARY OF THE INVENTION

The object of this invention is therefore to provide an electromagneticvalve which requires less electrical power than the heretofore knownelectromagnetic valve for controlling and stopping the flow of a liquidmetal or metal alloy in a pipe under load, and which introduces onlyslight disturbances in the flow when the valve is opened.

For this purpose, according to the present invention, theelectromagnetic valve for controlling the flow of a metal or metal alloyin liquid phase in a pipe under load comprises a tubular body made of amaterial permeable to the magnetic field and at least one polyphasefield coil arranged around the tubular body to create a magnetic fieldsliding along the longitudinal axis of the same tubular body. The valvecomprises a core which is maintained and extends axially in the tubularbody, the said core forms, between it and the inner wall of the tubularbody, a substantially annular passage for the liquid metal or metalalloy whose flow is to be controlled.

According to a preferred embodiment of this invention, the core can beformed by a magnetic bar embedded in a mass of material permeable to themagnetic field, with the core being connected to the tubular body of thevalve by radial arms made from the same material.

Although the reasons why the electromagnetic valve of this invention ismore efficient than the previously known electromagnetic valve are notfully elucidated, without wishing to be bound to any particular theory,it may be due to the fact that the magnetic flux generated by the fieldcoil is concentrated by the core provided in the tubular body, and theflow of liquid metal or metal alloy is confined in the annular regionbetween the core and the internal wall of the tubular body i.e., in aregion where the magnetic field is naturally more intense. Therefore,the magnetic field is more efficient at the annular region than at thecenter of the tubular conduit, because the annular region is closer tothe field coil which surrounds the tubular body.

BRIEF DESCRIPTION OF THE DRAWING

A non-limiting embodiment of the invention will be described withreference to the attached drawings, in which:

FIG. 1 is a schematic cutaway view of an electromagnetic valve inaccordance with the invention.

FIG. 2 is a half cutaway view along line II--II of FIG. 1. Theelectromagnetic valve shown in FIGS. 1 and 2 comprises, in a knownmanner, a tubular body 1 made of a material which is permeable to themagnetic field created by a polyphase field coil 2 which surrounds thetubular body 1, and which may be supplied with current by a source ofpolyphase current 3 with variable intensity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

If the electromagnetic valve is intended to control a flow of moltenmetal or metal alloy, the body 1 is preferably made of a refractorymaterial which is non-wettable by contact with the molten metal or metalalloy, for example, a ceramic material.

In addition, in such an embodiment, the tubular body is preferablyclosely surrounded over its whole length by a heating device 4 capableof heating the body 1 to a sufficient temperature to maintain the moltenmetal or metal alloy at a predetermined temperature higher than itsmelting temperature. The heating device 4 may be composed in a knownway, for example, of an electromagnetic induction heating device or byelectrical heating resistors.

On the other hand, if the metal or metal alloy is liquid at lowtemperature or ambient temperature, the body 1 does not need to be of arefractory material and may simply be made of a material permeable tothe magnetic field, which is stiff enough to ensure the mechanicalstrength of the valve body and compatible with the metal or a metalalloy passing through the valve.

The polyphase field coil 2 is placed and connected electrically so as tocreate a field sliding along the longitudinal axis of the tubular body 1in a direction such that the magnetomotive forces F exerted by thepolyphase field coil 2 on the liquid metal or metal alloy flowingthrough the tubular body 1 oppose the flow of the liquid metal or metalalloy, shown by the arrow G under the effect of the hydrostaticpressure. The polyphase field coil 2 can, for example, be composed of acoil of the type manufactured by the MADYLAM Laboratoire atSaint-Martin-d'Heres, France. If necessary, this field can be cooled ina known manner by a cooling fluid circulating in channels provided inthe coil. The current necessary for exciting the polyphase coil 2provided by the source 3 can be obtained, for example, from the 3-phasenetwork 380 V-50 Hz connected to a voltage lowering transformer capableof lowering the voltage to 17 V and itself coupled to the field coil 2by means of an intensity regulating device.

In accordance with the invention, a core 5 extends axially in thetubular body 1 and is held therein by several radial arms or flanges 6.The core 5 may have approximately the same length as the tubular body 1and the arms or flanges 6 may have the same length as the core 5 orextend only over a part of its length. Preferably, the core 5 andflanges 6 are profiled so as to generate the least possible disturbancesin the liquid metal or alloy flowing in the tubular body 1. For the samereasons, the inner diameter of the tubular body 1 and the outer diameterof the core 5 are chosen in such a way that the area of the annularsection of passage between the core 5 and the body 1 is equal to thearea of the circular section of the passage upstream and possiblydownstream of the electromagnetic valve. Preferably, the core 5 iscomposed of a magnetic bar 7 embedded in a mass 8 of material permeableto the magnetic field, this material being preferably the same as thatforming the arm or flanges 6 and the tubular body 1, for example, arefractory material non-wettable in contact with the liquid metal ormetal alloy. The magnetic bar 7 ensures the looping of the magneticfield generated by the polyphase field coil 2.

In the embodiment shown as an example in FIG. 1, the electromagneticvalve may include a second polyphase field coil 9 arranged and connectedelectrically so as to be able to play a role similar to that of thepolyphase field coil 2. The polyphase field coil 9 can be connected tothe current source 3, for example, by means of a switch 10, or it can beconnected to its own adjustable polyphase current source 11, as shown inbroken lines in FIG. 1. In the first case, the polyphase field coil 9doubly ensures the same function as the polyphase field coil 2 and canbe used as an emergency coil in the event of failure of coil 2. In thesecond case, a small leakage flow may possibly be allowed at the levelof the polyphase field coil 2, which small flow might then easily bestopped by the magnetic field created by the polyphase field coil 9. Theadvantage of this second arrangement is to further reduce theconsumption of energy necessary for completely stopping the flow ofliquid metal or metal alloy and to limit the size of the equipmentnecessary for supplying current to field coils 2 and 9.

At its inlet end, the tubular body 1 is equipped with a flange or otherconnecting means 12 by which the electromagnetic valve may be fixed tothe end of a pipe 13 for conveying liquid metal or metal alloy or to avessel containing the liquid metal or metal alloy. In the same way, atits outlet end, the tubular body 1 may also include a flange or otherappropriate connecting means 14 by which the electromagnetic valve maybe connected, if required, to another pipe 15 for transporting liquidmetal or metal alloy.

If the electromagnetic valve is intended to control the flow of a moltenmetal or metal alloy, the tubular body 1 or the pipe 15 mayadvantageously be equipped with an injector 16 allowing a controlledinjection of a neutral or inert gas avoiding oxidation of the liquidmetal or metal alloy trapped in the electromagnetic valve.

By way of example, with an electromagnetic valve whose body 1 has aninner diameter of 14 mm and a core 5 with an outer diameter of 8 mm andcomprising a sole polyphase field coil having 10 turns per phase with adiameter of 45 mm, it was possible to completely stop the flow of amolten zinc alloy, which was maintained at a temperature of 480° C., thehydrostatic pressure at the inlet to the electromagnetic valve being2.5×10⁴ Pa (0.25 bar). For that purpose, the polyphase field coil wassupplied with a current of 2400 A. (It should be noted that the assemblywith which the experiment was carried out was not optimized and did notinclude a device for regulating intensity. It may therefore be expectedthat the intensity of the current sufficient for causing the complete ofthe flow of molten zinc can be even lower than 2400 A). By way ofcomparison, with an electromagnetic valve with no central core, in orderto stop almost completely stop the flow of molten zinc alloy, it wouldhave been necessary to supply the field coil with a polyphase current ofan intensity at least four to five times greater.

It goes without saying that the form of execution of the electromagneticvalve described above has been given purely as an example and is by nomeans limitative, and that many modifications can easily be made byspecialists without departing from the scope of this invention.

I claim:
 1. An electromagnetic valve for controlling flow of a liquidmetal or metal alloy in a pipe under load, comprising:a tubular bodycomposed of a material permeable to a magnetic field, said tubular bodyhaving a longitudinal axis and an internal wall; at least one polyphasefield coil positioned around said tubular body capable of generating amagnetic field which is slidable along said longitudinal axis; and acore comprising a magnetic material, said core extending axially withinsaid tubular body to ensure looping of the magnetic field generated bysaid at least one polyphase field coil and defining a substantiallyannular passage with said internal wall for flow of the liquid metal ormetal alloy.
 2. The electromagnetic valve according to claim 1, whereinsaid core comprises a magnetic bar embedded in a mass of materialpermeable to the magnetic field.
 3. The electromagnetic valve accordingto claim 2, comprising radial arms for positioning said core withrespect to said internal wall.
 4. The electromagnetic valve according toclaim 3, wherein said radial arms are composed of material permeable tothe magnetic field.
 5. The electromagnetic valve according to claim 4,wherein said radial arms and said mass of material are composed of thesame material.
 6. The electromagnetic valve according to claim 1,wherein said at least one polyphase coil comprises two polyphase fieldcoils positioned around said tubular body.
 7. The electromagnetic valveaccording to claim 6, wherein said two polyphase field coils areconnected to a same source of current.
 8. The electromagnetic valveaccording to claim 6, wherein said two polyphase field coils areconnected to different sources of current.
 9. The electromagnetic valveaccording to claim 1, wherein said tubular body comprises a refractorymaterial.
 10. The electromagnetic valve according to claim 9, whereinsaid refractory material comprises a ceramic material.
 11. Theelectromagnetic valve according to claim 1, wherein said core and saidtubular body comprise substantially equal lengths.
 12. Theelectromagnetic valve according to claim 11, wherein said core comprisesa magnetic bar embedded in a mass of material permeable to the magneticfield.
 13. The electromagnetic valve according to claim 12, comprisingradial arms for positioning said core with respect to said internalwall.
 14. The electromagnetic valve according to claim 1, furthercomprising a heating element for heating said tubular body.
 15. Theelectromagnetic valve according to claim 1, further comprising aninjector element for controlled injection of an inert gas into theelectromagnetic valve while avoiding oxidation of the liquid metal ormetal alloy.
 16. The electromagnetic valve according to claim 14,wherein said core comprises a magnetic bar embedded in a mass ofmaterial permeable to the magnetic field.
 17. The electromagnetic valveaccording to claim 16, comprising radial arms for positioning said corewith respect to said internal wall.